Search PubMed⌕ Search

Biomedical subjects

A M Smith

Publications and source records attributed to A M Smith.

At least 127 records · Page 7Linked to original sources
PubMed1999

Neuronal activity in somatosensory cortex of monkeys using a precision grip. I. Receptive fields and discharge patterns.

Three adolescent Macaca fascicularis monkeys weighing between 3.5 and 4 kg were trained to use a precision grip to grasp a metal tab mounted on a low friction vertical track and to lift and hold it in a 12- to 25-mm position window for 1 s. The surface texture of the metal tab in contact with the fingers and the weight of the object could be varied. The activity of 386 single cells with cutaneous receptive fields contacting the metal tab were recorded in Brodmann's areas 3b, 1, 2, 5, and 7 of the somatosensory cortex. In this first of a series of papers, we describe three types of discharge pattern, the receptive-field properties, and the anatomic distribution of the neurons. The majority of the receptive fields were cutaneous and covered less than one digit, and a chi2 test did not reveal any significant differences in the Brodmann's areas representing the thumb and index finger. Two broad categories of discharge pattern cells were identified. The first category, dynamic cells, showed a brief increase in activity beginning near grip onset, which quickly subsided despite continued pressure applied to the receptive field. Some of the dynamic neurons responded to both skin indentation and release. The second category, static cells, had higher activity during the stationary holding phase of the task. These static neurons demonstrated varying degrees of sensitivity to rates of pressure change on the skin. The percentage of dynamic versus static cells was about equal for areas 3b, 2, 5, and 7. Only area 1 had a higher proportion of dynamic cells (76%). A third category was identified that contained cells with significant pregrip activity and included cortical cells with both dynamic or static discharge patterns. Cells in this category showed activity increases before movement in the absence of receptive-field stimulation, suggesting that, in addition to peripheral cutaneous input, these cells also receive strong excitation from movement-related regions of the brain.

Action Potentials↗
PubMed1999

Neuronal activity in somatosensory cortex of monkeys using a precision grip. II. Responses To object texture and weights.

Three monkeys were trained to lift and hold a test object within a 12- to 25-mm position window for 1 s. The activity of single neurons was recorded during performance of the task in which both the weight and surface texture of the object were systematically varied. Whenever possible, each cell was tested with three weights (15, 65, and 115 g) and three textures (smooth metal, fine 200 grit sandpaper, and rough 60 grit sandpaper). Of 386 cells recorded in 3 monkeys, 45 cells had cutaneous receptive fields on the index or thumb or part of the thenar eminence and were held long enough to be tested in all 9 combinations of texture and weight. Recordings were made for the entire anterior-posterior extent of the thumb and index finger areas in somatosensory cortex including area 7b. However, the statistical analysis required a selection of only those cells for which nine complete recording conditions were available limiting the sample to cells in areas 2, 5, and 7b. Significant differences in the grip force accompanied 98% of the changes in texture and 78% of the changes in weight. Increasing the object weight also increased the force tangential to the skin surface as measured by the load or lifting force. The peak discharge during lifting was judged to be the most sensitive index of cell activity and was analyzed with a two-way analysis of variance (ANOVA). In addition, peak cell discharge was normalized to allow comparisons among different combinations of texture and weight as well as comparisons among different neurons. Overall, the peak firing frequency of 87% of the cells was significantly modulated by changes in object texture, but changes in object weight affected the peak activity of only 58% of the cells. Almost all (17/18, 94%) of the static cells were influenced by the object texture, and 81% of the dynamic cells that were active only briefly at grip and lift onset were modulated by texture. For some cells, surface texture had a significant effect on neuronal discharge that was independent of the object weight. In contrast, weight-related responses were never simple main effects of the weight alone and appeared instead as significant interactions between texture and weight. Four neurons either increased or decreased activity in a graded fashion with surface structure (roughness) regardless of the object weight (P < 0.05). Ten other neurons showed increases or decreases in response to one or two textures, which might represent either a graded response or a tuning preference for a specific texture. The firing frequency of the majority (31/45) of neurons reflected an interaction of both texture and weight. The cells with texture-related but weight-independent activities were thought to encode surface characteristics that are largely independent of the grip and lifting forces used to manipulate the object. Such constancies could be used to construct internal representations or mental models for planning and controlling object manipulation.

Afferent Pathways↗
PubMed1999

Neuronal activity in somatosensory cortex of monkeys using a precision grip. III. Responses to altered friction perturbations.

The purpose of this investigation was to examine the activity changes in single units of the somatosensory cortex in response to lubricating and adhesive coatings applied to a hand-held object. Three monkeys were trained to grasp an object between the thumb and index fingers and to lift and hold it stationary within a narrow position window for 1 s before release. Grip forces normal to the skin surface, load forces tangential to the skin surface, and the displacement of the object were measured on each trial. Adhesive (rosin) and lubricant (petroleum jelly) coatings were applied to the smooth metal surface of the object to alter the friction against the skin. In addition, neuronal activity evoked by force pulse-perturbations generating shear forces and slip on the skin were compared with the patterns of activity elicited by grasping and lifting the coated surfaces. Following changes in surface coatings, both monkeys modulated the rate at which grip forces normal to the skin surface and load forces tangential to the skin surface were applied during the lifting phase of the task. As a result, the ratio of the rates of change of the two forces was proportionately scaled to the surface coating properties with the more slippery surfaces, having higher ratios. This precise control of normal and tangential forces enabled the monkeys to generate adequate grip forces and prevent slip of the object. From a total of 386 single neurons recorded in the hand area of the somatosensory cortex, 92 were tested with at least 1 coating. Cell discharge changed significantly with changes in surface coating in 62 (67%) of these cells. Of these coating-related cells, 51 were tested with both an adhesive and lubricating coating, and 45 showed significant differences in activity between the untreated metal surface and either the lubricant or the adhesive coating. These cells were divided into three main groups on the basis of their response patterns. In the first group (group A), the peak discharge increased significantly when the grasped surface was covered with lubricant. These cells appeared to be selectively sensitive to slip of the object on the skin. The second group (group B) was less activated by the adhesive surface compared with either the untreated metal or the lubricated surface, and they responded mainly to variations in the force normal to the skin surface. These cells provide useful feedback for the control of grip force. The third group (group C) responded to both slips and to changes in forces tangential to the skin. Most of these cells responded with a biphasic pattern reflecting the bidirectional changes in load force as the object was first accelerated and then decelerated. One hundred sixty-eight of the 386 isolated neurons were tested with brief perturbations during the task. Of these, 147 (88%) responded to the perturbation with a significant change in activity. In most of the cells, the response to the perturbation was shorter than 100 ms with a mean latency of 44.1 +/- 16.3 (SD) ms. For each of the cell groups, the activity patterns triggered by the perturbations were consistent with the activity patterns generated during the grasping and lifting of the coated object.

Animals↗
PubMed1999

Outcome of an opportunistic infection after polymicrobial peritonitis in an HIV-infected patient treated with peritoneal dialysis.

The prevalence of human immuodeficiency virus (HIV)-infected patients with end stage renal disease (ESRD) is likely to increase and many of them will be on peritoneal dialysis as renal replacement therapy. Infectious complications are a major problem associated with peritoneal dialysis (PD). It has been speculated that the HIV-positive peritoneal dialysis population may develop peritonitis more frequently than other peritoneal dialysis patients. We present the complications and unexpected good response to medical management of PD-associated peritonitis in a young HIV-infected black male. He had two unusual and serious infections; the first was a polymicrobial peritonitis which predisposed the patient to an unusual infection caused by Corynebacteria JK for which he was successfully treated without catheter removal.

AIDS-Related Opportunistic Infections↗
PubMed1999

Factors affecting men's liking of condoms they have used.

The objective of this study was to assess the impact on men's liking for the condoms they use of a range of factors including demographic variables and variables that describe men's experience of using particular condoms. One hundred and ninety-four men used 3765 condoms for which they provided a liking rating. The condoms were manufactured to one of 2 published standards and the study employed a double-blind crossover design. Sixty-one per cent of condoms were rated favourably, 31% were rated neutrally and the remainder (8%) unfavourably. Men rated condoms less favourably if they were experienced as too loose, too tight, too short, if difficulty was experienced applying the condom, if the condom slipped partially or completely down the penis or if the condom broke. Men rated more highly condoms which were experienced as well lubricated throughout use. Men with larger penises rated condoms less favourably and, of all the variables considered, ejaculating in the condom was the variable which had the largest positive impact. Men's liking for the condoms they use is influenced by a range of factors. However, given that most of the factors associated with men liking condoms less are those that can be addressed through better condom design and manufacture, the opportunity exists to enhance men's experience of condom use and hence help reduce resistance to the adoption of consistent condom use.

Adult↗
PubMed1999

Mapping the literature of dietetics.

Research on the literature of dietetics, apart from the broader field of nutrition, has not been reported in the literature. The purpose of this bibliometric study was to identify the core journals of dietetics and to determine the extent of indexing coverage for these journals. The study was conducted as part of a larger project, the Project for Mapping the Literature of Allied Health, sponsored by the Nursing and Allied Health Resources Section of the Medical Library Association. Citations appearing in three journals between 1995 and 1997 were analyzed by the methodology common to studies in the project. Results revealed that dietetic literature relies heavily on journal literature and on those journals that are from associated health sciences fields. Of the indexing services examined, EMBASE/Excerpta Medica and MEDLINE provided the most complete coverage of the literature. The study's findings have implications for those involved with the literature of dietetics.

Abstracting and Indexing↗
PubMed1998

Expression of CCKB/gastrin receptor isoforms in gastro-intestinal tumour cells.

Anti-serum raised against the human cholecystokinin B (CCKB)/gastrin receptor was used in Western blotting to differentiate the cellular locations of receptor isoforms expressed by human gastro-intestinal (GI) tumour cell lines. Using anti-serum directed against the amino-terminal extracellular tail of the CCKB/gastrin receptor, 8/9 cell lines were shown to express immunoreactive proteins of either m.w. 70 or 40 kDa, or both. Both isoforms were found to be associated with intracellular, non-nuclear membranes, whereas only the 70 kDa protein was expressed in the plasma membrane. Receptor expression was related to gastrin production and secretion. Both progastrin and glycine-extended gastrin-17 were produced and secreted by the tumour cell lines; however, carboxy amidated gastrin was not detected by radioimmunoassay. A CCKB/gastrin receptor transfectant NIH3T3 cell line did not produce detectable gastrin and showed exclusive expression of the 70 kDa receptor on the plasma membrane. One cell line had <50 pg/ml cell-associated progastrin and no detectable receptor form. Cell lines expressing 50-150 pg/ml had both 40 and 70 kDa receptor forms. Those expressing >150 pg/ml progastrin had only the 40 kDa isoform, which was shown to be exclusively expressed on intracellular, non-nuclear membranes, in one of the cell lines. Of the 4 cell lines exclusively expressing the lower m.w. receptor, 3 had gastrin present within the cell, which was not secreted. Thus, if cell-associated gastrin induces a proliferative effect, it may be by an intracrine pathway. Our study has identified the presence of CCKB/gastrin receptor isoforms in different cellular locations and may help toward understanding the complex autocrine and intracrine pathways mediated by gastrin peptides.

3T3 Cells↗
PubMed1998

Prevalence of IgG anti-Der p 2 antibodies in children from high and low antigen exposure groups: relationship of IgG and subclass antibody responses to exposure and allergic symptoms.

Serum IgG PAN, IgG1-4, and IgE antibodies (Ab) specific for the house dust mite Dermatophagoides antigen (Ag) Der p 2 were measured by enzyme-linked immunosorbent assay (ELISA) in two groups of school children, age 12-14, exposed to high (Charlottesville, VA) and low (Los Alamos, NM) mite Ag levels in their environment. More than 90% of the children were found to have Der p 2-specific IgG antibodies, although the levels of both IgG PAN and IgG 1-4 Ab were substantially higher in the high exposure group (P = 0.001). In addition, there was considerable overlap between these two groups in all Ab measurements. The presence of IgG anti-Der p 2 Ab in the Los Alamos children was unexpected and suggests continuing Ag exposure, although the source of such exposure is not apparent. There is no correlation between RAST (+) and RAST (-) subjects with respect to the level of IgG Ab measured by ELISA. These results suggest that the IgG Ab response to house dust mite has been underestimated in the RAST negative population. Two twin pairs were included in this study and the divergent and varied Ab responses in these individuals indicate that factors in addition to environmental exposure and genetic susceptibility require further investigation and provide evidence for the complexity of the pathogenesis of the allergic response.

Adolescent↗
PubMed1998

Quantitation of regional cerebral blood flow increases in prefrontal cortex during a working memory task: a steady-state arterial spin-tagging study.

Steady-state arterial spin-tagging MRI approaches were used to quantitate regional cerebral blood flow increases in prefrontal cortex during a working memory ("two-back") task in six normal subjects. Statistically significant increases in cerebral blood flow in prefrontal cortex were observed in all six subjects: the average increase in cerebral blood flow in activated prefrontal cortex regions was 22 +/- 5 cc/100 g/min (23 +/- 7%). The results demonstrate that spin-tagging approaches can be used to follow focal activation in prefrontal cortex during cognitive tasks.

Adult↗
PubMed1998

Regulation of tubulin polypeptides and microtubule function: Luv1p [correction of Rki1p] interacts with the beta-tubulin binding protein Rbl2p.

Genetic analysis of microtubule functions in the yeast Saccharomyces cerevisiae suggests that cells manage the levels and activities of the tubulin polypeptides. These reactions may be involved in protein folding, formation of the heterodimer, and maintenance of the appropriate balance between alpha- and beta-tubulin. One protein involved in these functions is Rbl2p, which forms a complex with beta-tubulin. Here we describe the identification of a novel yeast gene, LUV1 [corrected], that interacts genetically with RBL2. Deletion of rki1 causes conditional defects in microtubule assembly and cell growth. Luv1p [corrected] can be isolated in a complex containing Rbl2p. The results support the existence of cellular mechanisms for regulating microtubule function through the tubulin polypeptides.

Amino Acid Sequence↗
PubMed1998

Relationship of endogenous sex hormones to lipids and blood pressure in mid-aged women.

PURPOSE: The relationship between endogenous sex hormones and blood lipids was examined in a representative sample of 438 Australian-born women 45 to 56 years of age taking part in a longitudinal study of the menopausal transition. Data from 363 women who were taking neither exogenous hormones nor lipid-altering medications, were not diabetic, and who had provided blood samples were available for analysis. METHODS: Multiple linear regression was used to examine the relationship between sex hormones and high density lipoprotein cholesterol (HDL), low density lipoprotein cholesterol (LDL), triglycerides, and diastolic blood pressure (DBP), taking account of the effects of age, body mass index (BMI), smoking, alcohol intake, and exercise. RESULTS: There was no significant relationship between estradiol and HDL, LDL, triglyceride, or DBP levels. Free androgen index was positively associated with LDL. However, BMI was an important predictor of all three lipid measures and DBP. HDL was positively associated with age and was highest among women with lowest BMI, high alcohol intake, and in nonsmokers. LDL increased with BMI, free androgen index, and age, but was lower amongst women who exercised more than two or three times per week. Triglyceride also increased with BMI, and was higher among smokers. DBP increased with BMI only. CONCLUSIONS: The results do not support the view that endogenous sex hormones are strongly associated with cardiovascular risk factors around the time of menopause.

Androgens↗
PubMed1998

Australian and South African undergraduates' HIV-related knowledge, attitudes, and behaviors.

To understand safe sex behavior in two countries which have been differentially affected by the HIV/AIDS epidemic, the present study compared the AIDS-related knowledge, attitudes, and behaviors of 920 heterosexual undergraduate students in Australia and 228 heterosexual undergraduate students in South Africa. South African students were found to have significantly less knowledge about HIV/AIDS, and significantly less favorable attitudes toward safe sex behavior than their Australian counterparts. They were also more likely to report that they have avoided various groups of people for fear of contracting AIDS. Experience from Australia over the period 1986-1995 suggests that significant improvements in the AIDS-related knowledge, attitudes, and behaviors of South African undergraduates are achievable.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Gastric carcinoid expresses the gastrin autocrine pathway.

BACKGROUND: In gastric adenocarcinoma the gastrin autocrine-paracrine pathway is activated. As enterochromaffin-like (ECL) cells originate from the same stem as epithelial cells, the aim of this study was to determine if the gastrin autocrine pathway is present in gastric carcinoid. METHODS: Samples from ten patients with gastric carcinoid were assessed by immunocytochemistry using primary antibodies directed against gastrin precursors and the gastrin/cholecystokinin B receptor and detected using the avidin-biotin immunoperoxidase system. RESULTS: A high level of expression of precursor and mature gastrin peptides, together with the gastrin receptor, was seen in all carcinoids screened. CONCLUSION: In common with the glandular epithelium of the stomach the gastrin gene is activated during the neoplastic process in ECL cells. This finding may explain why some carcinoids do not regress after surgical procedures that lower serum gastrin. Antigastrin agents may be a useful treatment for carcinoid either in their own right or as an adjunct to surgery.

Adult↗
PubMed1998

A starch-accumulating mutant of Arabidopsis thaliana deficient in a chloroplastic starch-hydrolysing enzyme.

The aim of this work was to identify enzymes that participate in the degradation of transitory starch in Arabidopsis. A mutant line was isolated by screening leaves at the end of the night for the presence of starch. The mutant had a higher starch content than the wild-type throughout the diurnal cycle. This accumulation was due to a reduction in starch breakdown, leading to an imbalance between the rates of synthesis and degradation. No reduction in the activity of endo-amylase (alpha-amylase), beta-amylase, starch phosphorylase, maltase, pullulanase or D-enzyme could be detected in crude extracts of leaves of the mutant. However, native PAGE in gels containing amylopectin revealed that a starch-hydrolysing activity, putatively identified as an endo-amylase and present in wild-type chloroplasts, was absent or appreciably reduced in the mutant. This is the first time that a specific enzyme required for starch degradation has been identified in leaves.

Amylases↗